JPH1043842A - Tundish for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a cast slab excellent in the quality by reducing splash developed just after starting pouring from a ladle to a tundish and restraining the oxidation of molten steel just after starting casting. SOLUTION: A refractory-made weir 2 whose height H is in the range satisfying the inequality h0 >=H>=0.6× [1.312×(Q/R)<2> +1]<1/2> -1}, is arranged on the bedding 12 of the tundish 1 around a pouring point 3 of the molten steel 11, and the molten steel is stayed with the weir to prevent the development of splash. In the inequality, H0 is the inner height of the tundish at the weir setting position, Q is the max. molten steel pouring quantity into the tundish and R is the width of the weir. Then, a notching part 5 having a prescribed area and a through-hole 13 can be arranged in the weir.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tundish for continuous casting of steel, and more particularly, to a weir provided in a tundish to prevent molten steel from splashing immediately after injecting molten steel from a ladle into the tundish. It is related to the shape of.

[0002]

2. Description of the Related Art In a continuous casting of steel, a tundish lay (the bottom is the bottom of the inner surface) is generally formed by pouring molten steel from a ladle in order to reduce the amount of residual steel in the tundish at the end of casting. The point position is a position higher than the position of the outflow hole to the mold. As a result, immediately after the start of injection into the tundish, the area around the injection point is constantly exposed to the injection flow colliding with the floor, so that molten steel droplets (hereinafter, referred to as “splash”) are generated, and Until the molten steel surface rises to a molten steel depth at which the energy of the injected flow can be reduced.

[0003] The generated splash falls into the molten steel and re-melts, or adheres to the refractory on the side wall of the tundish and re-melts as the molten steel surface rises. Furthermore, it adheres and deposits on the back surface of the upper lid of the tundish. This splash is
It has a large specific surface area and easily reacts with oxygen in the atmosphere to increase the oxygen concentration, which is re-dissolved in the molten steel in the tundish.

Recently, in order to reduce the cost of refractories, used tundishes are not cold-repaired each time they are used, but the inner surface of the tundish is repaired as disclosed in, for example, JP-A-8-12288. So-called hot rotary use, in which the steel sheet is continuously reused in a hot state without being used, has been implemented. In the cold repair, the ingot metal on the side wall of the tundish and the back surface of the upper lid can be removed by scraping off or the like, so that there is no problem in quality and operation. On the other hand, in the case of hot rotating use, there is no method of efficiently removing the adhered metal at these sites, and a method of melting and discharging the adhered metal with a gas burner is generally used. However, in this method, the base metal is oxidized during the melting process, and the base metal containing a large amount of oxide adheres to and remains on the tundish floor, which is redissolved when it is received from the ladle. The slab quality deteriorates significantly. In addition, if the adhered metal is left, the amount of adhesion gradually increases, the weight of the tundish in the tare increases, and a predetermined amount of molten steel cannot be secured in the tundish,
Eventually, quality and operational problems arise, such as the inability to operate. Therefore, various methods for solving these problems have been proposed.

For example, Japanese Unexamined Utility Model Publication No. 58-57356 (hereinafter referred to as "prior art 1") discloses a technique in which the inside of a tundish is replaced with an inert gas such as Ar. According to the prior art 1, it is described that the splash can be prevented from being oxidized, and at the same time, the injection flow from the ladle and the oxidation of the molten steel in the tundish can be prevented, so that a highly clean cast slab can be obtained.

Japanese Unexamined Patent Publication No. 64-34551 (hereinafter referred to as "prior art 2") discloses a weir made of an iron plate having a height higher than a lower end position of a long nozzle on a tundish bed immediately below the long nozzle. And a method in which the lower end of the long nozzle is immersed in molten steel stored in a weir and injected. According to the prior art 2, since the tip of the long nozzle is immersed at an early stage, the generation of splash is suppressed and air oxidation is also prevented, and the iron plate weir melts and disappears due to the heat of molten steel. There is no upward flow due to the weir, and no slag floating on the surface of the molten metal is involved in the upward flow, so that it is said that slabs of good quality can be obtained.

[0007]

In prior art 1, it is possible to prevent the oxidation of the splash, but it is not possible to prevent the occurrence of the splash. Further, in the prior art 2, the molten steel is cooled by the iron plate weir, the temperature of the molten steel decreases, and there is a possibility that the nozzle may be clogged at the outflow hole and the immersion nozzle.
In addition, since the lower limit of the weir height is unknown, there is a risk that the weir height will be excessively high, and since a long long nozzle is also required,
This leads to an increase in weir and refractory costs. Further, in a tundish that uses hot rotation, it is difficult to install a weir in a high-temperature tundish by hand, and a dedicated facility for installing the weir is required, resulting in an increase in manufacturing costs.

[0008] The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a continuous casting tundish having a weir which is inexpensive and can be operated stably, and has a weir suitable for preventing the occurrence of a splash which can be applied even in a hot rotating use. .

[0009]

According to a first aspect of the present invention, there is provided a tundish for continuous casting of steel, in which a molten steel pouring point from a ladle is positioned higher than a pouring hole into a mold. In a tundish for continuous casting of steel in which a refractory weir is provided on a surrounding floor, the height of the weir satisfies the expression (1). Ho ≧ H ≧ 0.6 × ｛[1.312 × (Q / R) ² +1] ^1/2 −1｝ …… (1)

Here, in the formula (1), each symbol represents the following. H: Weir height (cm) Ho: Tundish inner surface height at the position of the weir (cm) Q: Maximum amount of molten steel injected into the tundish (liter /
Min) R; Weir width (cm)

If a tall weir is provided in the vicinity of the injection point of the tundish bed, the inside of the tundish on the injection point side of the weir (hereinafter, the inside of the tundish on the injection point side of the weir will be referred to as "in the weir")
Molten steel stays in the area, preventing the occurrence of splash. However, if the height of the weir is excessively high, the cost of the refractory constituting the weir increases, which is not reasonable and is not necessary during steady casting. A strong ascending flow of molten steel, deteriorating the quality,
Since the amount of molten steel staying in the weir increases, the molten steel load applied to the weir in the early stage of casting increases, and there is a high possibility that the weir will fall down during use. Therefore, the weir is the minimum height that prevents the occurrence of splash. It is necessary.

The present inventors conducted a water model experiment in order to find the minimum weir height in which molten steel injected from a ladle into a tundish did not climb over a weir provided near the injection point and stayed in the weir. investigated. As a result, the following three points became clear. : The injected water violently engulfs the atmospheric gas at the injection point, causing water to splash. : Only the injection point position is not the position where the droplets are generated. : As the injected water flows through the tundish floor,
Atmospheric gas is entrapped in a region where the flow velocity is slow, as schematically shown in FIG. 2, so-called "Hydraulic jump".
A phenomenon called "water bulkiness" occurs.

From the above investigation results, it was presumed that if a weir having a height equal to or higher than the water jump height was installed, the injected water would not climb over the weir, but would accumulate in the weir and prevent the generation of water droplets. As shown in FIG. 2, the water jump height h is expressed by equation (3) as a function of the Froude number, where g is the gravitational acceleration when water flows at a speed u and a liquid film thickness d of the tundish bed. That is, for example, the "Civil Engineering Hydr" of JRDFancis etc.
aulics, (1984), p. 289 ". In the equation (3), Fr is the Froude number defined by the equation (4) on the upstream side of the weir. h = (d / 2) × [(8 × Fr ² +1) ^1/2 −1] …… (3) Fr = u / (g × d) ^1/2 …… (4)

The jump height according to the equation (3) can be calculated by the following procedure. The maximum molten steel injection rate from the ladle into the tundish is Q (liter / min), the weir width is R (cm),
The liquid film thickness is d (cm) and the molten steel flow rate on the tundish bed is u
(Cm / sec) and the gravitational acceleration is g (cm / sec ² ), the flow rate u of molten steel on the tundish can be obtained from equation (5). u = (1000 × Q) / (60 × R × d) …… (5)

Here, the liquid film thickness d was estimated from the experimental results of the present inventors on molten aluminum, and in the case of a steel actual tundish, the liquid film thickness d was a constant value of 1.2 cm. Assuming that the gravitational acceleration is 980 cm / sec ² , the Froude number Fr is calculated from the obtained molten steel flow velocity u by the equation (4), and the Froude number Fr is substituted into the equation (3) to jump the water for various injection amounts and weir widths. Height can be calculated. The maximum amount of molten steel injected into the tundish is the maximum flow rate when pouring molten steel into the tundish at the start of casting.
The reason for calculating the water jump height from the maximum molten steel injection amount is that the water jump height becomes maximum when the injection amount is maximum.

Next, the validity of the equation (3) was examined using a 1/3 scale water model apparatus. Similarity rule agreement is similar to Froude number. The Froude number similarity means that an experiment is performed under the condition that the value of [velocity / (gravity acceleration × distance) ^1/2 = Froude number] is the same between the model and the actual machine.
In the model experiment, the flow velocity is 1
/ 3, length 1/3, area 1/9, volume 1/27
Becomes Incidentally, the liquid film thickness in the 1/3 model is 0.4 cm.

The weir width R in the actual machine is 108 cm, the height of the inner surface of the tundish at the position where the weir is installed is 90 cm, and the amount of molten steel injected from the ladle into the tundish at the start of casting is 17 tons / min at maximum. When this molten steel injection amount is converted into a molten steel specific gravity of 7.0 g / cm ³ , the maximum molten steel injection amount Q is 2429 liters / minute. According to the similarity rule in the 1/3 model, the maximum injection amount to the tundish is 155 liters / minute. And the flow rate of water in the model experiment was set at a fixed amount of 155 liter / min.

FIG. 3 schematically shows a tundish in the 1/3 model. As shown in FIG. 3, the weir is placed over the entire width of the tundish at a position 20 cm away from the injection point to the outlet hole side, and the injection point is 15.5 cm from the tundish wall opposite to the outlet hole side. It is far away. The weir width corresponding to the actual machine is 36 cm, but the tundish width at the position where the weir is installed is 30 cm, 35 cm and 40 cm, that is, the weir width is 30 cm.
The test was performed by changing to three levels of cm, 35 cm and 40 cm. The diameter of the injection pipe corresponding to the long nozzle of the actual machine is 3 cmΦ.
With the model set in this way, the weir height H was changed to 8.5 cm, and the scattering of water droplets was investigated.

The scattered water droplets were collected and measured, and the measured values were compared. FIG. 4 shows the results of indexing and comparing the amount of splash generated when the height of the weir is changed with the amount of splash generated when there is no weir set to 1.0. As shown in FIG. 4, in the water model experiment, it can be seen that as the height of the weir increases, the amount of generated water drops decreases. If the droplet generation index is set to 0.2 or less, the weir height to achieve the target is 6.0 cm or more for a weir width of 30 cm, 5.0 cm or more for a weir width of 35 cm, and 4.0 for a weir width of 40 cm. 0 cm or more.

The maximum molten steel injection amount Q is 155 liters /
For three cases with a weir width of 30 cm, 35 cm, and 40 cm, the flow velocity on the tundish floor was obtained from equation (5), and the Froude number was obtained from equation (4). The jump height h in the model experiment was calculated by substituting into the equation. The calculation result shows that when the weir width is 30 cm, h =
At 5.95 cm and 35 cm, h = 5.07 cm, and at 40 cm, h = 4.42 cm. The calculated values are also shown in FIG. Then, as shown in FIG. 4, it can be seen that the weir height at which the amount of generated droplets is 0.2 or less in the water model experiment matches well with the calculated value of the equation (3). That is, it can be confirmed that when the weir height is higher than the water jump height calculated by the equation (3), the generation of the splash can be prevented, and that the splash prevention effect is not further improved in the range where the weir height exceeds the water jump height. Was.

The result of the above water model is also applicable to the case of molten steel of an actual machine.
When the speed in equation (5) and the Froude number in equation (4) are substituted into equation (3), the equation for estimating the water jump height h of molten steel in an actual machine is obtained as equation (6). . h = 0.6 × ｛[1.312 × (Q / R) ² +1] ^1/2 -1… …… (6)

If the height H of the weir to be installed is not less than the height h of the water jump determined from the equation (6), the outflow from the weir due to the water jump can be prevented, and the molten steel can be retained in the weir. The right-hand inequality in equation (1) that determines the lower limit of the height is derived.

The purpose of the weir is achieved if a sufficient amount of stagnation can be secured to alleviate the energy of the injection flow. Even in the result of the water model, even if the weir height is higher than the water jump height calculated by the equation (3), the effect of preventing the generation of the splash does not improve any more, so the weir height H is calculated by the equation (6). It is not necessary to make the height significantly higher than the jumping water height, and at most a half or less of the tundish inner surface height (Ho) at the position where the weir is installed is sufficient. Further, it is desirable to keep the value within 10 cm from the value of the expression (6), in order to suppress the upward flow of the molten steel which is unnecessary in terms of the cost of the refractory, and also to prevent the weir from collapsing.

The tundish for continuous casting of steel according to the second invention is the tundish for continuous casting of steel according to the first invention, wherein the weir has a notch, and the notch width satisfies the expression (2). It is characterized by doing. (20000 × M) / (V × t ₁ × H) ≦ w ≦ R × [1− (60 × M) / (q × t ₂ )] (2)

However, in the formula (2), each symbol represents the following. w: notch width (cm) H: weir height (cm) q: average molten steel injection amount into tundish (liter / liter)
Min) R; Weir width (cm) V; Average discharge speed of molten steel from cutout of weir (cm /
S) M; weir in the molten steel amount when weir in the molten steel becomes a weir height (l) t _1; melt surface in the tundish residual molten steel time required to complete the discharge from the time of the weir lower end position (s) t ₂ : Set time (second) from the start of injection into the tundish

If there is no notch in the weir, molten steel remains in the weir at the end of casting, and the steel yield decreases. However, if the notch width is too large, molten steel does not accumulate in the weir at the start of casting, and splash cannot be prevented. The present inventors presumed that this problem would be solved if a notch with an optimum width was provided in the weir, examined it, and confirmed it with a water model.

[Examination of Minimum Value of Notch Width] The minimum value of the notch width can be obtained by preventing molten steel from remaining in the weir at the end of casting. Then, the conditions under which molten steel does not remain in the weir at the end of casting were considered as follows.

The state in which molten steel is discharged from the cutout of the weir is assumed as shown in FIG. The discharge speed from the notch is a speed based on a static pressure difference generated by the molten steel height Z in the weir.
Then, the discharge speed becomes maximum when the molten steel height Z in the weir is the maximum H, and becomes minimum zero when there is no molten steel in the weir.
It is assumed that the molten steel discharge speed from the weir is represented by these average values, and the molten steel height Z in the weir, which is substantially the average value, is [weir height H ×
[1/2] was taken as the average discharge speed V.
The cross-sectional area to be discharged was a cross-sectional area formed by the height of 1/10 of the height Z of the molten steel in the weir and the notch width w. Then, the average value of the molten steel height Z in the discharging weir is [weir height H × 1
/ 2], the average value of the discharge cross section is [(weir height H
X 1/20) x notch width w].

Then, it is assumed that the molten steel in the weir must be discharged from the weir within the required time from when the molten steel surface of the residual molten steel in the tundish shown in FIG. did. Then, the average discharge speed of molten steel from the notch of the weir is V (cm / sec), and the notch width is w (c
m), the required time (hereinafter, referred to as “required time”) from the time when the molten steel surface of the residual molten steel in the tundish is discharged to the end of the weir (hereinafter referred to as “the required time”) is t ₁ (second), and the molten steel in the weir is the weir height Assuming that the amount of molten steel in the weir at the time of contact is M (liter), the amount of molten steel M in the weir within t ₁ hour is the cross-sectional area [(weir height H × 1/20) ×
The notch width w] must flow out of the weir at the average discharge speed V. When this is expressed by an equation, the equation (7) is obtained. 1000 × M ≦ (V × w × H × t ₁ ) / 20 …… (7)

By modifying equation (7), the left-hand inequality of equation (2) is obtained, and the minimum value of the notch can be obtained. When there are a plurality of notches, the notch width w is a value obtained by summing the plurality of widths.

[Study of Maximum Notch Width] In order to quickly store molten steel in the weir at the start of casting, it is not good to make the notch width too large. Therefore, it is assumed that molten steel stays in the weir even when there is a notch as follows.

It is assumed that the molten steel speed per unit width passing through the tundish bed is constant regardless of the presence or absence of the weir.
That is, it is assumed that the molten steel stays in the weir in proportion to the weir width obtained by subtracting the notch width. Based on this assumption, the amount of molten steel in the weir when the molten steel in the weir reaches the weir height is M (liter), the average amount of molten steel injected from the long nozzle into the tundish is q (liter / min), and the width of the weir Is R (cm) and notch width is w
(Cm), assuming that a set time from the start of injection into the tundish (hereinafter referred to as a “set time”) is t ₂ (seconds), it is necessary to store M or more of molten steel in the weir within t ₂ hours. No. When this is shown by the equation, the equation (8) is obtained. M ≦ (q / 60) × [(R−w) / R] × t ₂ …… (8)

By transforming equation (8), the inequality on the right side of equation (2) is obtained, and the maximum width of the notch can be obtained.
The reason why the average value is used as the amount of molten steel injected into the tundish at the start of casting is that, in order to store a predetermined amount of molten steel in the weir, the maximum value or the minimum value is inaccurate.

[Results of Water Model] The validity of equation (2) is
Investigation was carried out with a water model device of / 3 scale. Similarity rules were matched by Froude number similarity. The 1/3 tundish is shown in FIG. 3 and is the same as that in which the weir height was studied, and the weir width was set at three levels of 30 cm, 35 cm and 40 cm. However, the weir height was kept constant at 5 cm for each level.

The average molten steel injection rate q into the tundish in the actual machine is 1429 liters / minute (10 tons / minute).
In the 1/3 model, it becomes 92 liters / minute. The required time t ₁ in the actual machine is 40 tons of residual steel in the tundish,
At the end of the casting, the casting is finished except for 4 tons, and the casting speed is 7 tons / min. In the 1/3 model,
According to the similarity rule, the required time is 1/1/1 of the required time t ₁ of the actual machine.
3, that is, 178 seconds, the amount of drainage from the outlet was controlled so that the required time was 178 seconds.

The set time t ₂ was determined from the state of splash generation in the actual machine. FIG. 6 is a result of investigating the state of splash occurrence every 5 seconds from the start of casting to a tundish without a weir. It can be seen from FIG. 6 that as the time elapses, the amount of splash generated per unit time decreases, and the occurrence of the splash is mostly up to about 20 seconds after the start of the injection. Therefore, in order to prevent the occurrence of the splash, it is necessary to make the molten steel stay in the weir a predetermined amount at a time considerably earlier than 20 seconds after the start of the injection. Therefore, in the present invention, the set time is set to 10 seconds. Since the time of splash generation depends on the amount of molten steel injected and the shape of the tundish, it is desirable to set the set time by investigating the state of splash generation with each continuous casting machine. Applicable to machines. The set time in the case of the 1/3 model is 1/3 of the set time of the actual machine, that is, 5.8 seconds according to the similarity rule.

Under the above conditions, in a 1/3 water model,
Weirs with different notch widths were installed around the injection point, and the amount of water splashing and the residual water in the weir at the end of casting were investigated.
The investigation results are shown in FIGS. FIG. 7 shows the result of investigation of the residual water amount in the weir at the end of casting, and FIG. 8 shows the result of investigation of the amount of splash generated at the beginning of casting. From FIG. 7, the minimum value of the notch width becomes smaller as the weir width becomes smaller. However, if the minimum width is set to 2 cm or more, the residual water amount can be made zero in a water model experiment up to the weir width of 40 cm. 8, the range of the notch width where the droplet generation index is 0.2 is 12 cm for a weir width of 30 cm.
cm or less, a weir width of 35 cm is 10 cm or less, and a weir width of 40 cm is 8 cm or less.

Further, the weir volume and the average discharge rate in the 1/3 model are calculated, and from these calculated values and the above conditions,
When the minimum width and the maximum width of the notch in the 1/3 model experiment are calculated by the equation (2), the minimum width is 1.7 cm for a weir width of 30 cm, 2.0 cm for a weir width of 35 cm, and 2.0 cm for a weir width of 40 cm. 2.3 cm, and the maximum width is 12.0 when the weir width is 30 cm.
cm, weir width is 10.5cm at 35cm, weir width is 7.9 at 40cm
cm.

FIGS. 7 and 8 also show these calculated values. From these calculated values, although the range of the results of the experiment using the water model satisfying the purpose is slightly wider, (2)
The range according to the expression is within the range of the result of the water model. If it is at least within the range of the expression (2), it is possible to prevent splash at the start of casting and prevent the generation of residual steel in the weir at the end of casting. I understand.

The tundish for continuous casting of steel according to the third invention is the tundish for continuous casting of steel according to the first invention, wherein the weir has a notch and a through hole or a through hole. At least one of the through-holes is in contact with the tundish pad, and the notch and the total cross-sectional area of the through-hole or the through-hole have a weir height defined by the formula (1) and a cut-off defined by the formula (2). It is characterized by being equal to the total cross-sectional area determined as the product of the notch width.

The present inventors also investigated the amount of water splashing and the amount of residual water in the weir at the end of casting using a 1/3 water model for a weir having a through hole in addition to the notch.
The weir width was 35 cm, and the weir height was 5 cm, which is the lower limit of the equation (1). The conditions in the water model are the same as the conditions for examining the minimum and maximum values of the notch width.

Two types of notches, type B and type C, shown in FIG. 9 and through holes were provided in the weir. Type B has two notches having the same width as the flow path, and a through hole having a cross-sectional area equal to the cross-sectional area of one notch is provided at the center, and type C has the same width. With two notches,
Two through-holes having a cross-sectional area equal to one-half of the cross-sectional area of one notch are provided at the center, and these through-holes are in contact with the tundish floor. The test was performed such that the cross-sectional area of the through-hole was always 1/3 of the total cross-sectional area. Type A shown in FIG. 9 is a weir used for comparison, in which only three notches are provided as flow paths, and the widths of the three notches are equal.

FIGS. 10 and 1 show the results of the investigation using the water model.
It is shown in FIG. FIG. 10 shows the result of investigating the amount of residual water in the weir at the end of casting, and FIG. 11 shows the result of investigating the amount of splash generated at the beginning of casting. It can be seen from FIG. 10 that Type B and Type C have better discharge efficiency of residual water in the weir than Type A. This is because in the type B and the type C, the discharge efficiency from the through hole in contact with the floor is good. Since the minimum width of the notch according to the equation (2) is 2.0 cm as described above, the calculated minimum cross-sectional area defined as the product of the weir height and the minimum width of the notch is 10 cm ² , which is also shown in FIG. However, as shown in FIG. 10, if the total cross-sectional area of the notch and the through hole provided in the weir is equal to or larger than the calculated minimum cross-sectional area, it is possible to prevent the generation of residual steel in the weir at the end of casting. I understand.

As shown in FIG. 11, in the types B and C, as compared with the type A, as the total cross-sectional area of the flow path becomes larger, the amount of generated water drops increases. 5cm) and the maximum width of the notch by equation (2) (10.5
cm) calculated maximum cross-sectional area (52.5c)
m ² ) Below, it can be seen that there is not much difference in the amount of water generated. This is because the width (w ₃ ′, w ₃ ″, w ₄ ′) of the through-hole needs to be larger than the height (H ′) when the total cross-sectional area of the flow path increases. Although the amount of outflow from the hole increases, a through-hole having the same size as the notch can be provided near the calculated maximum cross-sectional area. It can be understood that, if is set to be equal to or less than the calculated maximum sectional area, splash at the start of casting can be prevented.

That is, the total cross-sectional area of the notch and the through-hole or the through-hole is determined by the product of the weir height defined by the equation (1) and the notch width defined by the equation (2). If the cross-sectional area is made equal, the generation of residual steel in the weir at the end of casting can be prevented, and the splash at the start of casting can be prevented. The purpose of contacting the through hole and the floor is to prevent residual molten steel from remaining in the weir at the end of casting.

[0046]

FIG. 1 illustrates an embodiment of the present invention.
I will tell. FIG. 1A shows the tundish of the present invention.
The front view, FIG. 1 (b) and FIG. 1 (c) show X in FIG. 1 (a).
FIG. 1B is a cross-sectional view of FIG.
Fig. 1 (c) shows a cutout and a through hole in the weir.
This is the case. In the figure, 1 is a tundish, 2
Is a refractory weir, 3 is an injection point from a ladle, 4 is an outflow hole,
5 is a cutout of a weir, 6 is a long nozzle, 7 is a dipping nozzle.
, 8 is the top lid of the tundish, 9 is the ladle, 10 is the casting
A mold, 11 is molten steel, 12 is a floor, and 13 is a through hole. Tan
The position of the pouring point 3 is the position of the outflow hole 4
The height of the tundish 1 is higher than the
It is inclined from the 3 side to the outflow hole 4 side. w₁, W_Two, W_Three
Is the width of the notch 5, w _Three′ Is the width of the through hole 13.

The flow of the molten steel 11 from the ladle 9 falls through the long nozzle 6 to the injection point 3 and stays in the weir 2. The retained molten steel 11 overflows the weir 2 and is immersed in the outflow hole 4. It is cast into a mold 10 via the nozzle 7. At the start of casting, the molten steel 11 is retained in the weir 2 to reduce the energy of the injected flow to prevent the generation of splash. At the end of casting, the cutout 5 and the through hole 13 of the weir 2 allow the molten steel 11 to enter the weir 2. Of molten steel 11 is discharged. In such a structure of the tundish 1, the specifications of the present invention are determined by the following procedure.

[Procedure 1]: The installation position of the weir 2 is determined. Although the weir 2 can be installed at an arbitrary position from the injection point 3, in order to make the molten steel 11 stay in the weir 2 quickly,
The distance from the injection point 3 (the distance of J shown in FIG. 1) is 30 cm
It is desirable that the thickness be in the range of 100 to 100 cm. In the case of less than 30 cm, the amount of retained molten steel in the weir 2 is insufficient to reduce the energy of the injection flow, and in the case of more than 100 cm, the rising speed of the retained molten steel 11 becomes slow, and the prevention of the generation of splash is delayed. Inconvenient. Once the location of the weir 2 is determined,
The weir width R and the amount of residual molten steel in the tundish 1 when the molten steel level in the tundish 1 at the end of casting reaches the lower end position of the weir 2 are determined. The required time t ₁ is determined from the residual molten steel amount and the casting amount in the mold. Further, the set time t ₂ is different from the splash generation period depending on the tundish 1 to be used. Therefore, it is desirable to determine the set time t ₂ by investigating the state of the splash generation in the casting without using the weir 2, but if the set time is 10 seconds, Can be applied to most tundishes 1 without any problem.

[Procedure 2] Since the amount of molten steel injected into the tundish 1 at the start of casting differs depending on the capacity of the tundish 1, the amount of molten steel injected into the tundish 1 to be used is grasped. At this time, the maximum molten steel injection amount Q into the tundish 1 and the average molten steel injection amount q are distinguished and grasped. When the injection amount is stable and constant, the maximum value and the average value can be the same.

[Procedure 3] First, the lower limit of the weir height H is calculated from the right side of the equation (1) based on the above conditions. Then, the height of the weir 2 to be installed is determined to be an arbitrary height that satisfies the right side of the expression (1) and is と or less of the inner surface height of the tundish 1 at the installation position of the weir 2.

[Procedure 4] When the weir height H is determined, the amount M of molten steel in the weir is obtained from the distance k and the distance j shown in FIG. or,
By determining the weir height H, the average discharge speed V from the weir 2 is calculated as a value at half the height of the weir 2.

[Procedure 5]; Substituting the above conditions into equation (2), calculating the minimum and maximum values of the notch width, and setting the notch width w to an arbitrary value between the minimum value and the maximum value. Decide as. When only the notch 5 is installed, the number of the notches 5 and the installation position of the notch 5 are arbitrarily determined from the determined notch width w, and are installed on the weir 2. FIG. 1B shows a case where the number of the cutouts 5 is 3, and the cutouts 5 are installed at the center and both sides of the weir 2. When the notch 5 and the through hole 13 are provided, the product of the set weir height H and the set notch width w is calculated, and the notch 5 and the through hole 13 provided on the weir are calculated.
The number of the notches 5 and the through holes 13 and the respective cross-sectional areas are arbitrarily determined so that the total cross-sectional area becomes equal to the product of the weir height H and the notch width w. At that time, the through hole 1
At least one of the three is provided in contact with the tread 12 of the tundish 1.

[Procedure 6]: The weir 2 having the notch 5 or the notch 5 or the notch 5 and the through hole 13 is set in the tundish 1 in this manner, and casting is started. I do.

In the above description, the description of the case where only the through-hole 13 is provided is omitted, but in that case, the procedure may be performed in accordance with the case where the notch 5 and the through-hole 13 are provided in [Procedure 5]. FIG. 1 shows a single-strand tundish 1. However, in the case of a tundish 1 having two or more multi-strands and having an outflow hole 4 to a mold 10 on both sides of an injection point 3, the injection point 3 The present invention can be applied by installing the weirs 2 on both sides of.

[0055]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a tundish having the structure shown in FIG.
Type A weir shape with only three notches installed in the weir (implementation
Example 1) and Type B weir type with notches and through holes
The present invention was carried out in the same manner (Example 2). Cast molten steel
Means that 250 tons of carbon per heat is less than 0.04 wt%
Continuous casting of more than 2 heat with carbon aluminum killed steel
Was. Tundish capacity is 80 tons, pouring point from ladle
46 cm from the tundish side wall opposite the outlet
Distance (distance k in Fig. 1), weir is 60cm from the injection point on the outflow hole side
The distance R (distance j in FIG. 1), the weir width R is 10
8cm, the level of molten steel in the tundish is at the bottom of the weir
The amount of residual molten steel in the tundish at that time is 40 tons. Dam
The inside height of the tundish at the placement position is 90 cm. Casting
The maximum value Q of molten steel injection into the tundish at the start of
2426 l / min, average value q is 1429 l / min
Minutes. At the end of casting, the remaining steel in the tundish is 4 tons.
The casting is finished at the end of the process.
/ Min, so the required time t ₁Is 309 seconds. Sp
Set time t to minimize rush generation_TwoIs 10
Seconds.

When the height H of the weir is obtained from these conditions from the equation (1), a weir height of 14.9 cm is obtained. From this calculated value, the tundish weir height was determined to be 15 cm. Then, from the tundish weir height, the amount M of molten steel in the weir when the molten steel in the weir reaches the weir height is found to be 169 liters.
From the height of the weir, the average discharge speed V from the weir can be calculated as 121 cm / sec.

When the minimum value and the maximum value of the notch width are obtained from the equation (2) under the above conditions, the minimum value of the notch is 6.0c.
m and a maximum value of 31.4 cm were obtained. In this embodiment, the notch width w was set to 30 cm. In Example 1, a notch of 10 cm was provided at the center and both sides of the weir. In Example 2, cutouts of 10 cm each were formed on both sides, and a through hole having a width of 15 cm and a height of 10 cm was placed in contact with the floor at the center. The material of the weir is high alumina brick.
For comparison, casting without a weir (conventional example)
The conditions other than the weir were the same as in the example. In addition, the inside of the tundish was not replaced with an inert gas,
In continuous casting with two heats, the amount of molten steel passing through the mold is about 1
Ladle replacement is performed after the passage of 70 tons. The results obtained from the investigation during and after casting are shown below.

FIG. 12 shows the results of the splash occurrence frequency obtained by photographing the casting situation and performing image analysis processing as a comparison of the index with the conventional example being 1. When the conventional example is set to 1, the frequency of occurrence of splash is clearly reduced in the present embodiment as compared with the conventional example, which is 0.22 in the embodiment 1 and 0.20 in the embodiment 2.

FIG. 13 shows the sol. [Al] and the total oxygen content (T [O]) of the molten steel component from the start of the molten steel injection into the tundish.
And the transition of the total nitrogen amount (also referred to as T [N]) is shown by collecting an analysis sample from within the mold and examining the results.
As shown in the figure, in this embodiment, the decrease in sol. [Al] at the start of the injection and the pickup of the total oxygen amount and the total nitrogen amount also decreased in comparison with the conventional example. This is because in the case of the present embodiment, the hot water pool was formed early, and the oxidation in the tundish was reduced. Also, in the period when the amount of molten steel passed through the mold from 40 tons to 170 tons after the start of casting, the total oxygen amount in the so-called steady casting portion is clearly smaller in this embodiment. This is because the floating of nonmetallic inclusions in the tundish was promoted by installing the weir. In addition, when changing the ladle (the amount of molten steel passing through the mold is 170 tons or more)
Is smaller in the present embodiment. This is because the short-circuit flow of the molten steel in the tundish caused by the decrease in the amount of molten steel in the tundish during ladle replacement was suppressed by the weir.

FIG. 14 shows a microscopic sample taken from a slab.
The result of having investigated the transition of the nonmetallic inclusion generation | occurence | production index of the slab by the molten steel passage amount in a mold is shown. In the embodiment, immediately after the start of pouring (the amount of molten steel passing through the mold is 0 to 40 tons), a steady portion (the amount of molten steel passing through the mold is 40 to 170 tons), and the ladle changing section (170 to 2)
Inclusion index at 50 tons) is 1 /
At 2 or less, it was better than the conventional example.

FIG. 15 shows a comparison of the transition of the weight of a tundish tare depending on the number of casting heats in a conventional example and an example in a hot rotating tundish which was left without removing the adhered metal. In the example, the change in the tare weight after using 400 heats was 10 tons, while in the conventional example, it was 12 tons at 150 heats, and the change in the tare weight of the tundish was smaller in the example than in the conventional example. It can be seen that the adhesion of the ingot was suppressed.

FIG. 16 is a graph showing the occurrence of product defects due to non-metallic inclusions in the thin steel sheet obtained by rolling the slabs obtained in the embodiment and the conventional example into thin steel sheets. It is a figure which classified and classified into the slab), the steady part slab, and the ladle exchange part slab. The example shows that the present invention reduces the product defect rate and improves the yield with a product defect occurrence rate of 1/2 of the conventional example.

Further, according to the present invention, the number of times of use of the hot rotating tundish can be continuously used exceeding 400 times. However, in the conventional method, the weight of the tare is increased, so that the continuous use is at most 200 times. It was times.

[0064]

According to the present invention, since the splash generated immediately after the start of pouring from the ladle into the tundish can be reduced, the oxidation of molten steel immediately after the start of casting is suppressed, and a high quality cast slab is produced. Can be. In addition, the adhesion of the base metal to the inner surface of the tundish and the back surface of the upper lid due to the splash is reduced, and in the tundish using hot rotation, the number of continuous use of the tundish is improved, and the life of the refractory can be extended. Furthermore, the weir promotes the floating and separation of nonmetallic inclusions in the tundish, and can improve the cleanliness of the slab of the stationary part and the ladle exchange part.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an embodiment of the present invention;
(A) is a front view, (b) and (c) are XX sectional views of (a).

FIG. 2 is a diagram schematically showing a situation in which a water jump phenomenon occurs.

FIG. 3 is a diagram schematically showing a 1/3 scale tundish water model device.

FIG. 4 is a diagram showing a comparison between a result obtained by investigating an effect of a weir height on a water droplet generation index by a 1/3 water model and a calculated value of a minimum weir height by equation (1). It is.

FIG. 5 is a diagram showing an assumption of a state of discharging from a notch in order to estimate a flow rate discharged from the notch of a weir.

FIG. 6 is a diagram showing a transition of a splash generation index per unit time after the start of pouring into a tundish in the case of a tundish without a weir of a continuous casting machine.

FIG. 7 shows the results of investigating the effect of the notch width on the amount of residual water in the weir at the end of casting under the condition of a constant weir height using a 1/3 water model, and the maximum notch of the weir according to equation (2). It is the figure which showed and compared with the calculated value of small width.

FIG. 8 shows the result of investigating the effect of the notch width on the water droplet generation index under a constant weir height condition using a 1/3 water model, and the calculation of the maximum width of the weir notch according to equation (2). It is a figure which showed by comparing with a value.

FIG. 9 is a schematic view of a weir provided with notches and through holes.

FIG. 10 is a diagram showing a result of investigating an influence of a shape of a flow path provided in a weir on a residual water amount in the weir at the end of casting using a ３ water model.

FIG. 11 is a diagram showing the results of an investigation of the influence of the shape of the flow path provided in the weir on the water droplet generation index using a 1/3 water model.

FIG. 12 is a diagram showing a splash occurrence frequency index in an example according to the present invention in comparison with a conventional example.

FIG. 13 is a diagram showing the transition of the components of sol. [Al], T [O], and T [N] with respect to the amount of molten steel passing through the mold in the example according to the present invention in comparison with the conventional example.

FIG. 14 is a diagram showing a transition of an index of the amount of inclusions generated in a slab with respect to a passing amount of molten steel in a mold in an example according to the present invention, in comparison with a conventional example.

FIG. 15 is a diagram showing a comparison of changes in the weight of a tundish tare according to the number of casting heats in an example according to the present invention and a conventional example.

FIG. 16 is a diagram showing a comparison between a product defect occurrence index due to non-metallic inclusions in an example according to the present invention and a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tundish 2 Weir 3 Injection point 4 Outflow hole 5 Notch 6 Long nozzle 7 Dipping nozzle 8 Top lid 9 Ladle 10 Mold 11 Molten steel 12 Floor 13 Through hole

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Noriko Kubo, Inventor 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Japan Co., Ltd. (72) Inventor Toshio Ishii 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor: Jun Kubota, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan (72) Inventor: Shin Suzuki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside the corporation

Claims (3)

[Claims] 1. A tank for continuous casting of steel in which the position of the molten steel pouring point from the ladle is higher than the position of the outflow hole to the mold, and a refractory weir is provided around the molten steel pouring point. A tundish for continuous casting of steel, wherein the height of the weir satisfies the formula (1). Ho ≧ H ≧ 0.6 × {[1.312 × (Q / R) ² +1] ^1/2 −1} (1) In the equation (1), each symbol represents the following. H: Weir height (cm) Ho: Tundish inner surface height at the position of the weir (cm) Q: Maximum amount of molten steel injected into the tundish (liter /
Min) R; Weir width (cm) 2. The tundish for continuous casting of steel according to claim 1, wherein the weir has a notch, and the notch width satisfies the expression (2). (20000 × M) / (V × t ₁ × H) ≦ w ≦ R × [1− (60 × M) / (q × t ₂ )] (2) However, in the formula (2), each symbol is as follows: Is represented. w: notch width (cm) H: weir height (cm) q: average molten steel injection amount into tundish (liter / liter)
Min) R; Weir width (cm) V; Average discharge speed of molten steel from cutout of weir (cm /
S) M; weir in the molten steel amount when weir in the molten steel becomes a weir height (l) t _1; melt surface in the tundish residual molten steel time required to complete the discharge from the time of the weir lower end position (s) t ₂ : Set time (second) from the start of injection into the tundish 3. The weir has a notch and a through-hole or a through-hole, at least one of the through-holes being in contact with a tundish bed, and a total of the notch and the through-hole or the through-hole. 2. The continuous steel according to claim 1, wherein the cross-sectional area is equal to a total cross-sectional area defined as a product of a weir height defined by the equation (1) and a notch width defined by the equation (2). 3. Tundish for casting.